Two part intersomatic implant

ABSTRACT

A spinal implant comprising a hollow body having a leading end, a trailing end and a pair of lateral walls extending from the leading end to the trailing end, the lateral walls including concave, non-threaded inner surfaces defining an internal space of the hollow body. The implant includes an anchoring member insertible between the lateral walls and into the internal space of the hollow body, the anchoring member having bone anchoring projections defining an outer diameter of the anchoring member. When the anchoring member is inserted into the internal space of the hollow body, the concave inner surfaces of the lateral walls substantially conform to the outer diameter of the anchoring member.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/192,457, now allowed, which is a continuation of U.S. patentapplication Ser. No. 10/131,741, now U.S. Pat. No. 6,855,168, which is acontinuation of U.S. patent application Ser. No. 09/403,396, filed Feb.15, 2000, now abandoned, which claims priority under 35 U.S.C. 371 ofPCT/FR98/00825, filed Apr. 24, 1998, the disclosures of which are herebyincorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates generally to intersomatic implants whichcan be used in the surgical treatment of the spine.

A great many intersomatic implants are already known. These include, inparticular, implants made up of several parts, particularly to give theimplants certain deformability characteristics. These known implantshave the disadvantage of being more expensive and difficult tomanufacture, and more awkward to fit. These implants can also sufferfrom long-term reliability problems.

In order to overcome some of the above-mentioned disadvantages, certainimplants are provided in the form of one-piece hollow bodies, or cages,having roughened areas on their upper and lower faces in order to ensuregood initial immobilization relative to the overlying and underlyingvertebral plates. The hollow bodies permit bone to grow through theimplant for fusing the implant to vertebral bone. One such implanthaving a hollow body is disclosed in FR-A-2,703,580.

These known one-piece implants, despite the presence of roughened areaswhich become anchored in the vertebral plates, may suffer frominadequate stability in some cases. This is because the quality of theanchoring, which is effected by a simple translational movement, dependson the hardness of the bones.

Other implants have an outer body and an inner anchorage reinforcementelement that is screwed into the outer body. The threads of theanchorage reinforcement element project above and below the upper andlower faces of the outer body.

One object of the present invention is to improve this type of knownimplant.

SUMMARY OF THE INVENTION

An implant for surgery of the spine includes an essentially hollow bodyinsertable into an intervertebral space defined by opposing vertebrae.The body has a pair of lateral walls enclosing an internal space exposedto the overlying and underlying vertebrae. The implant also includes ananchorage reinforcement member that is screwed into the internal spaceof the hollow body. The anchorage reinforcement member has externalthreads or bone anchoring projections having a diameter greater than theoverall height of the body. The external threads may be self-tappingscrew threads or have a generally square radial cross-section.

To counter the reverse movement of the body out of the intervertebralspace, and hence to further improve the securing of the implant inposition, the hollow body has upper and lower surfaces provided withsharp-edged teeth which can be anchored in the vertebrae. The teethpreferably have a triangular cross-section.

According to another preferred embodiment of the present invention, inorder to improve the compactness of the implant and to make it easier toput into place, the lateral walls of the hollow body are partiallycylindrical and coaxial with an axis of the anchorage reinforcementmember.

According to yet another preferred embodiment of the invention, thelateral walls have through-openings permitting bone to grow throughthem. These through-openings preferably include elongate slots extendingsubstantially parallel to the direction of insertion of the anchoragereinforcement member into the hollow body.

In order to give the body a greater width, it is possible to use, forthe lateral walls of the body, thick walls in which secondthrough-openings are formed, extending between the upper and lower facesof the body. Bone growth can also be induced between the two vertebralplates via these second through-openings.

The first through-openings preferably bring the internal space intocommunication with the second through-openings.

It is also possible to provide through-openings which bring the secondthrough-openings into communication with the outer sides of the body.

According to another preferred embodiment of the invention, the hollowbody has a distal end wall connecting the lateral walls. The distal endwall is rounded to facilitate insertion of the hollow body into theintervertebral space.

The invention also preferably includes an implant as described above, inwhich the hollow body has a distal end wall connecting the lateralwalls. The distal end wall has a tapped hole for temporarily fixing thehollow body to an instrument for facilitating insertion of the body.

This screw thread of the anchorage reinforcement member preferably has aradial cross-section which changes progressively from an essentiallytriangular radial cross-section to the generally square radialcross-section starting from the distal end of the thread, whereby thediameter of the screw thread increases progressively, starting from itsdistal end, up to a part of essentially constant diameter. In otherwords, the screw thread has a radial cross-section that transforms froma beveled distal end to a substantially square radial cross-section.

According to another preferred embodiment of the invention, an implantis also proposed in which the projections for bone anchorage comprise ascrew thread in the form of a helical band encircling an internal spaceof the anchorage reinforcement member.

The helical band is advantageously connected to a fork extending insidethe band in an axial direction of the member, and this fork preferablycomprises two branches extending from a proximal end wall of theanchorage reinforcement member.

The fork may also include branches having a frustoconical externalsurface, the diameter of which decreases from the proximal end towardsthe distal end of the member. This makes it possible to compress asubstance promoting bone growth, placed beforehand in the anchoragereinforcement member, when the latter is being screwed in.

Alternatively, the fork includes at least two branches, each having acutting edge for cutting or biting into bone, in order thereby toaccumulate bone chips inside the member 20 and facilitate bone fusion.It is preferable for the fork and the helical band to be made in onepiece.

The invention also proposes an implant in which the projections for boneanchorage include a screw thread, whereby the anchorage reinforcementmember has structure for immobilizing the latter against reverserotation. The immobilizing structure preferably includes a deformed partof the thread in the region of its proximal end, which improves thestability of the implant until fusion has taken place.

According to another preferred embodiment of the present invention, theprojections for bone anchorage include a screw thread having an externaldiameter which decreases from the proximal end toward the distal end inorder to make it easier for the screw thread to penetrate the vertebralplates.

In another preferred embodiment, the anchorage reinforcement member hasa proximal end wall which is able to essentially close a frontal openingof the hollow body in such a way that a substance for promoting bonegrowth, placed inside the member, is compressed during the insertion ofthe member into the hollow body.

In this embodiment, the anchorage reinforcement member has at least onepart whose external surface belongs to a truncated cone. Alternatively,the anchorage reinforcement member is substantially shorter than thebody and has a generally conical point directed towards the distal endwall of the body.

It is advantageous in this case that the proximal end wall of the memberhas a tapped opening for temporarily fixing the member to an instrumentfor inserting the member.

According to yet another preferred embodiment of the present invention,the anchorage reinforcement member has indexing means for fixing themember to an instrument for inserting the member in a given angularrelationship.

According to another preferred embodiment, the anchorage reinforcementmember has a plug attached at its proximal end. The plug can, forexample, be screwed into a tapped frontal opening of the anchoragereinforcement member, or else can be engaged by being clippedelastically into a frontal opening of the anchorage reinforcementmember.

The plug preferably has an arrangement which can cooperate with aninstrument allowing the member to be driven in rotation, and/orarrangements for angular indexing of the anchorage reinforcement memberwith an instrument for positioning the member.

It is also proposed according to the invention that the projections forbone anchorage include a screw thread, and that at least one of thelateral branches of the body has a reentrant part forming a threadingwhich is able to cooperate with the thread. This reentrant part can beprovided only on one of the branches and can constitute the only part ofthe body cooperating, by screwing, with the screw thread. In addition,this reentrant part can have an essentially rectilinear free end edge.

According to another preferred embodiment, the invention proposes animplant in which the member is oriented obliquely, for example at about45°, in relation to a plane of the body corresponding to the sagittalplane.

According to another preferred embodiment, the anchoring member hasthrough-openings provided in the member between the interior and theexterior thereof. The openings are elongate in an essentiallycircumferential direction of the member.

According to another preferred embodiment of the present invention, thebody has a distal end wall, and the anchorage reinforcement member has adistal end part which can be screwed into an opening of the distal endwall.

The body can also have a proximal end wall including an opening which iswider than the external dimension of the anchorage reinforcement memberand in which the member can be engaged freely.

The invention furthermore proposes an implant in which the body has aproximal wall, a distal wall and two lateral walls, the walls definingtherebetween an internal space which is larger than the anchoragereinforcement member. This assembly increases the space designated forbone growth between the overlying and underlying vertebral plates.

The anchorage reinforcement member may have a threaded part for screwingit into the proximal wall of the body. In other preferred embodiments,the anchorage reinforcement member and the distal wall of the body mayhave threaded structure cooperating with each other for fixing themember to the body.

In such a configuration, the projections for bone anchorage can comprisea screw thread having the same pitch as the threaded part or thethreaded means for fixing to the body.

The shape of the body, in this case, is preferably such that the lateralwalls and the proximal wall of the body extend essentially on the samearc of a circle, and that the distal wall is essentially rectilinear.

It is also advantageous that the upper and lower faces of the body haveprojections for bone anchorage which extend along its walls.

According to another preferred embodiment of the invention, an implantis provided with mounting structure for mounting the anchoragereinforcement member so that it can rotate in the internal space of thebody, while at the same time preventing relative translational movementbetween the hollow body and the anchorage reinforcement member.

The mounting structure preferably includes a cylindrical opening formedin a distal end wall of the body, and a shaft provided on the member andable to be engaged, by elastic deformation, in the opening.

In this particular embodiment, the anchorage reinforcement memberpreferably has the shape of a screw having two diametrically oppositeflats, with the projections for bone anchorage being defined between theflats, and cutting edges being provided at the transitions between thethread of the screw and the flats in order to promote bone fusion oncethe implant has been put into place.

To facilitate the insertion of the implant, the distance between theopposite flats is not greater than the distance between the upper andlower faces of the body.

According to another preferred embodiment, of the invention, an implantfor surgery of the spine includes an essentially hollow body which canbe inserted into an intervertebral space, the body having a group ofgenerally parallel walls defining at least two internal spaces situatedside by side and exposed to the overlying and underlying vertebrae whichdefine the intervertebral space. The implant additionally has at leasttwo anchorage reinforcement members having, on their external surface,projections for bone anchorage having a diameter greater than theoverall height of the body, the said anchorage reinforcement membersbeing adapted to be threaded into respective internal spaces of thebody.

In this particular embodiment, the anchorage reinforcement members arepreferably identical. The invention furthermore proposes that the hollowbody can have different geometries. In one preferred embodiment, theupper and lower surfaces of the hollow body are inclined in relation toone another, with a distance between them which decreases from theproximal end towards the distal end of the body. In another preferredembodiment, the upper and lower surfaces of the hollow body are inclinedin relation to one another, with a distance between them which decreasesfrom a first lateral side of the body towards the opposite lateral side.

The invention furthermore proposes a set of implants for forming aspinal implant intended to be inserted into an intervertebral space ofthe human vertebral column by being adapted to the geometry of theintervertebral space. This set of implants includes a plurality ofhollow bodies, each having a pair of lateral walls defining an internalspace and each able to be inserted into an intervertebral space in sucha way that the internal space is exposed to the overlying and underlyingvertebrae which define the intervertebral space. Each of the hollowbodies preferably has a specific size and shape, at least one anchoragereinforcement member having, on its external surface, projections forbone anchorage having a diameter greater than the overall height of thebodies. The anchorage reinforcement member is able to be driven inrotation in the internal space of any one of the bodies, in such a waythat a specific hollow body appropriate to the particular configurationof a given intervertebral space can be chosen from among the pluralityof hollow bodies.

The specific sizes and shapes of the bodies may vary. Certain preferredbodies have different angles of inclination between their upper andlower surfaces. Other preferred bodies have different widths. The widesthollow bodies preferably have lateral walls in which through-openingsare formed which extend between the upper and lower faces of the bodies.The hollow bodies may also have different heights and different lengths.

Regardless of their size or shape, the hollow bodies are preferablyadapted to receive the same type of anchorage reinforcement member.

The invention also proposes a method for positioning, in anintervertebral space of a human vertebral column, an implant includingan essentially hollow body having a pair of lateral walls enclosing aninternal space, and an anchorage reinforcement member having, on itsexternal surface, projections for bone anchorage having a diametergreater than the overall height of the body, and adapted to be driven inrotation in the internal space of the body. The method preferablyincludes selecting a hollow body from a set of hollow bodies havingdifferent shapes and dimensions. The selected hollow body is preferablyadapted to fit with the configuration of the intervertebral space. Themethod also includes filling the selected hollow body with a substancewhich promotes bone growth, pushing the hollow body into theintervertebral space in such a way that the internal space thereof isexposed to the overlying and underlying vertebrae which define theintervertebral space, and inserting the anchorage reinforcement memberinto the hollow body in such a way that the projections of the boneanchorage member anchor in the overlying and underlying vertebrae.

In embodiments where the intention is to position an implant whose bodyhas lateral walls provided with through-openings extending between theupper and lower faces of the body, the method can additionally include,before the step of pushing the hollow body into the intervertebralspace, a step in which the through-openings are filled with a substancewhich promotes bone growth.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, aims and advantages of the present invention will becomemore apparent on reading the following detailed description of preferredembodiments thereof, given by way of example, and with reference beingmade to the attached drawings, in which:

FIG. 1 is a perspective view of an implant according to a firstembodiment of the invention.

FIG. 2 is a side view of the implant of FIG. 1 placed between twovertebral plates.

FIG. 3 is a front view of the implant of FIG. 1.

FIG. 4 is a plan view of the implant of FIGS. 1 and 3.

FIG. 5 is a side view of an element of the implant of FIG. 1.

FIG. 6 is an end view in the direction of arrow VI in FIG. 5.

FIG. 7 is an end view in the direction of arrow VII in FIG. 5.

FIG. 8 is a perspective view of the element of FIGS. 5 to 7.

FIG. 9 is a perspective view of an implant according to a secondembodiment of the invention.

FIG. 10 is a front view of the implant of FIG. 9.

FIG. 11 is a plan view of the implant of FIGS. 9 and 10.

FIG. 12 is a plan view of a first element of the implant of FIGS. 9 to11.

FIG. 13 is a side view of a second element of the implant of FIGS. 9 to11.

FIG. 14 is an end view in the direction of arrow XIV in FIG. 13.

FIG. 15 is an end view in the direction of arrow XV in FIG. 13.

FIG. 16 is an exploded perspective view of an implant according to athird embodiment of the invention.

FIG. 17 is a side view of the implant of FIG. 16, when the implant isassembled.

FIG. 18 is a plan view in the direction of arrow XVIII in FIG. 17.

FIG. 19 is a view in the direction of arrow XIX in FIG. 17.

FIG. 20 is an exploded perspective view of an implant according to afourth embodiment of the invention.

FIG. 21 is a side view of the implant of FIG. 20, when the implant isassembled.

FIG. 22 is a view in the direction of arrow XXII in FIG. 21.

FIG. 23 is a view in the direction of arrow XXIII in FIG. 21.

FIG. 24 is an exploded perspective view of an implant according to afifth embodiment of the invention.

FIG. 25 is a side view of the implant of FIG. 24, when the implant isassembled.

FIG. 26 is a view in the direction of arrow XXVI in FIG. 25.

FIG. 27 is a view in the direction of arrow XXVII in FIG. 25.

FIG. 28 is an exploded perspective view of an implant according to avariant of the third embodiment of the invention.

FIG. 29 is a perspective view of the implant of FIG. 28 in the assembledstate.

FIG. 30 is a view of the rear of the implant of FIG. 29.

FIG. 31 is a side view of the implant of FIG. 29.

FIG. 32 is a plan view of the implant of FIG. 29.

FIG. 33 is a perspective view, before assembly, of an alternative designof the third embodiment of the invention.

FIGS. 34 to 36 are three perspective views of the body of thealternative design shown in FIG. 33.

FIG. 37 is an end view, from the distal direction, of the body of FIGS.34-36.

FIG. 38 is a perspective view of the anchorage reinforcement member ofFIG. 33.

FIG. 39 is a side elevational view of the anchorage reinforcement memberof FIG. 33.

FIGS. 40 and 41 show two perspective views of the implant of FIG. 33 inthe assembled state.

FIG. 42 is a plan view of the implant of FIG. 40.

FIG. 43 is a side elevational view of the implant of FIG. 40.

FIG. 44 is an end view, from the proximal direction, of the implant ofFIG. 40.

DETAILED DESCRIPTION

Where possible, identical or similar elements or parts are designated bythe same reference labels.

The terms “proximal” and “distal”, used throughout the presentdescription correspond, respectively, to that end of the implant nearestthe surgeon during a fitting operation and the end of the implantfurthest from the surgeon.

Referring to FIGS. 1-8, a cage-type intersomatic implant is shown whichis made up of two parts, namely a body 10 and an anchorage reinforcementmember 20.

The body 10 has the general shape of a ring, with an upper face 11, alower face 12, an inner face 13 and an outer face 14.

The contour of the body 10 has a circular shape truncated by a part ofrectilinear contour, its width being equal, for example, to aboutfour-thirds of its depth.

Along the rectilinear contour part, on the upper and lower faces 11 and12, roughened areas are formed to ensure that the implant is immobilizedrelative to the overlying V1 and underlying V2 vertebral plateaus orplates (see FIG. 2) when the implant is compressed between these.

The roughened areas are in the form of three upper ribs 11 b and threelower ribs 12 b, of triangular cross-section and of circulartrajectories concentric with the circular contour part of the body.

Opposite the rectilinear contour part, the body has a thicker wall,produced by an upper land and a lower land.

Formed in this wall part there is a tapped-through orifice 18 whose axisextends obliquely, and preferably at about 45°, relative to the verticalplane perpendicular to the plane distal wall of the implant, whichvertical plane corresponds to the sagittal plane.

In addition, the axis of this orifice 18, which extends essentiallyhorizontally, passes substantially through the center of the circularcontour part, going towards the opposite region situated at thetransition between the circular contour part and the rectilinear contourpart.

The implant according to the invention additionally includes theanchorage reinforcement member 20 adapted to reinforce the anchoring onthe vertebral plateaus.

In the embodiment shown in FIGS. 1-8, the member 20 includes a hollowcylindrical core 21 having a helical thread 22 on the outer surfacethereof that is threadable into the internal thread formed in theorifice 18.

Formed between the adjacent thread sections there are a plurality ofopenings 23, oblong in the direction of the helical run of the thread,for reasons explained below.

At its distal end, the member 20 is closed by a solid wall 25. At itsproximal end, the member 20 includes a solid part 24 in which there isformed a hollow recess 24 a, for example of hexagonal cross-section, forintroduction of a screwing instrument (not shown).

It is important to note, as is shown in particular in FIG. 3, that theoverall diameter D within which the thread 22 of the member 20 isinscribed is slightly greater than the overall height H within which thebody 10 is inscribed, for reasons which are explained below.

The length of the member 20 is such that it can be screwed into theorifice 18 of the body 10 until the outer face of its proximal solidpart 24 is substantially aligned with the outer face 14 of the body 10adjoining the orifice.

In certain preferred embodiments, the implant is positioned betweenvertebrae after the vertebrae have been distracted and a portion of theintervertebral disc has been removed. The body 10 of the implant,without its member 20, is put into the disc space, by an anterior orposterior approach. The internal space of the body is preferably firstfilled with bone graft material in order to ensure eventualintervertebral fusion by osteogenesis.

The contour of the body 10, with the flat in the proximal part, is suchthat it is easily inscribed within the surface area of a vertebralplateau. If necessary, it is possible to offer the surgeon bodies 10having different sizes, the particular size being selected as a functionof the spinal anatomy of the patient, as will be seen in greater detailbelow.

The two vertebrae are then released, and an initial immobilization ofthe body between the vertebral plateaus V1 and V2 is ensured with theaid of the ribs 11 b, 12 b.

The member 20 is then screwed into the orifice 18 with the aid of aninstrument. During this movement, the crest of the thread 22, whichprojects slightly upwards and downwards in relation to the crest partsof the ribs 11 b, 12 b, cuts into the opposing faces of the overlyingand underlying vertebral plateaus in the manner of a self-tapping screw,and thus affords a supplementary anchoring which will firmly immobilizethe implant relative to these plateaus.

In addition, the rotation of the member 20 as it penetrates the internalspace of the body 10 ensures that some of the bone graft material packedin the internal space will migrate through the openings 23 and into theinternal space of the hollow member 20. As a result, bone growth willalso be obtained through the member 20, and this will advantageouslyimmobilize the member 20 in terms of any rotation, particularly reverserotation, that risks affecting the stability of the implant in the longterm. Alternatively, it is also possible for the member 20 to be filledbeforehand with bone graft material.

FIGS. 9 to 15 illustrate a second embodiment of the present invention.

In these figures, elements or parts which are identical or similar tothose in FIGS. 1 to 8 are designated by the same reference labels, andonly the differences between this second embodiment and the first willbe described.

It will first be noted that the body 10, which has the same contour asin the case of FIGS. 1 to 8, has a wall of essentially constantthickness over its whole periphery.

Instead of the tapped-through orifice 18 in the first embodiment, thisbody includes a smooth-through orifice 19.

Moreover, a cylindrical rod 16 provided with a thread 16 a extends alongthe axis of the orifice 19 starting from the opposite region of the body10, situated essentially at the transition between its circular contourand straight contour parts.

In addition, the member 20, which has substantially the same externalcontour as in the case of the first embodiment, is solid, except for acentral bore 28 which opens out on its rear face and in which there isformed an internal thread 28 a complementary to the thread 16 a formedon the protruding rod 16 of the body.

It will be observed here that the helical pitch of the thread 16 a andof the associated internal thread 28 a is chosen substantially orexactly equal to the helical pitch of the thread 22 which is stillpresent on the outer surface of the member 20.

A frustoconical part 27 is provided around the mouth of the bore 28.

The member 20 has, on its front face, a screwing arrangement whichpreferably includes a projecting head 26, such as a head having ahexagonal cross-section.

The implant according to this second embodiment is used essentially inthe same way as that explained above.

The essential difference lies in the fact that the member 20 is screwedonto the rod 16 in the manner of a nut, the size of the orifice 19 beingchosen so as not to form an obstacle to this screwing. In this respectit suffices to choose an orifice 19 with a diameter slightly greaterthan the overall diameter of the thread 22. The frustoconical part 27 ofthe member 20 makes it easier to introduce the rear end of the memberinto the orifice 19 prior to screwing.

As the pitch of the thread 16 a is the same as that of the thread 22,the advance of the member 20 into the body 10, at the same time as themember is being driven in rotation, is such that the thread 22 here onceagain bites into the vertebral plateaus in the manner of a self-tappingscrew.

In certain preferred embodiments, the upper and lower annular faces 11and 12 of the body 10 extend in planes which are slightly oblique inrelation to each other, so as to adapt to the shape of theintervertebral space in question. Thus, as will be seen below, thesurgeon may be provided with bodies 10 having different inclinations inorder to adapt to the anatomy of the vertebrae which are to be treated.

The embodiment shown in FIGS. 9 to 15 is advantageous in that theexternal contour of the member 20 can be given a slightly frustoconicalshape in such a way that the amount by which the thread 22 projectsrelative to the crests of the ribs 11 a and 11 b remains essentiallyconstant from the front to the rear of the implant, and because thevertebral faces concerned are substantially parallel to the upper andlower faces of the body 10, the anchoring afforded via the thread isessentially of the same magnitude from the proximal end to the distalend.

Referring now to FIGS. 16 to 19, an implant according to anotherpreferred embodiment includes a body 10 which, in horizontal section,has the general shape of a U, with a bottom 101, or distal wall, and twoessentially parallel lateral walls or branches 102, 103. The bodyincludes upper and lower U-shaped faces 104 and 104′, respectively, onwhich there are formed bone anchorage teeth 105, 105′, respectively. Thebone anchorage teeth are sharp-edged teeth of triangular profile, whichfulfill a role analogous to that of the ribs 11 b in the precedingembodiments. Referring to FIG. 17, the upper and lower faces 104, 104′converge slightly towards one another from the trailing end to theleading end 10 of the hollow body.

The distal wall 101 has a tapped bore that permits temporary fixing ofan instrument (not shown) for fitting the body in the intervertebralspace.

The branches 102, 103 define a generally cylindrical internal space, forreasons explained below.

The two lateral branches 102, 103 of the body each include a respectivelongitudinal through-slot 106 and 107 for permitting lateral bonegrowth.

The proximal end of the body 10, remote from its distal end 101, has agenerally circular opening delimited by a reentrant thread 108 providedat the proximal free ends of the two branches 102, 103.

The implant includes an anchorage reinforcement member 20 provided witha hollow core whose outer surface is slightly frustoconical, taperingfrom its proximal end towards its distal end. A continuous thread 22 isformed on the outer surface of the core 21.

The thread 22, in the form of a helically configured flat band,cooperates with the reentrant thread 108 of the body 10 to allow themember 20 to be screwed inside the body.

As shown in FIG. 16, the core 21 is made up of three angularly offsetlongitudinal branches which are separated by longitudinal empty spaces23.

Each of the branches includes a leading edge including a cutting edge 21a. As the member 20 is rotated, the cutting edge 21 a scrapes the bonematerial from the overlying and underlying vertebrae. In this way,screwing in the member 20 will allow the internal space of the implantto be filled with bone chips, something which will help the graft totake and which will finally fuse the two vertebrae by means of bonegrowth.

The external diameter of the thread 22 is preferably very similar to theinternal diameter of the body 10, so that when the member 20 is beingscrewed in, it is guided inside the body.

The member 20 includes a proximal part 24 forming a bushing, the member20 including an opening which is delimited by a plurality of bosses 24 bseparated by recessed zones 24 c. The bosses 24 b, which constitute thestart of the branches 21 of the core, have an internal thread on theirinner surface.

The implant also includes a generally cylindrical plug 30 having, on itsouter surface, a thread 31 which is able to cooperate with the internalthread defined by the bosses 24 b. The rear face 32 of the plug isprovided with a recessed socket 32 a for a screwing instrument.

When inserting the implant into a disc space, the body 10, without themember 20, is positioned between vertebrae. The member 20, without itsplug 30, is filled with bone graft material via its rear opening. Theplug 30 is then put into place in the rear opening to prevent the bonegraft material from escaping. The member 20, provided with its plug, isthen screwed into body 10 with the aid of a screwing instrument engagedin the socket 32 a. During this operation, the thread 22 of the member20 anchors in the opposing surfaces of the overlying and underlyingvertebrae, possibly cutting off bone chips. In addition, the cuttingedges 21 a of the three branches 21 of the core of the member 20 attackthe vertebrae so as to cut off chips which will complete the filling ofthe internal space of the member 20. As the core 21 of the member 20advances, its frustoconical shape ensures compression of some of thisbone material against the walls of the vertebrae, in order to assist thegrafting.

FIGS. 20 to 23 illustrate a fourth embodiment of the invention in whichthe body 10 is similar to that described in FIGS. 16 to 19. In thisparticular embodiment, however, only branch 102 of the body is providedwith a through-slot 106, while the other branch 103 does not have one.This type of body is advantageously used when two implants are placed inthe same intervertebral space. In this case, the implants are arrangedside by side in such a way that the respective slots of the two bodiesare situated on the inside, in order to promote fusion with bone graftmaterial placed in the region of the intervertebral space situatedbetween the two implants.

In this preferred embodiment, the anchorage reinforcement member 20includes a threaded plug that is substantially shorter than the body 10in the axial direction. The member has a solid cylindrical core 21provided with a thread 22 which is able to cooperate with the thread 103of the body 10.

The rear face of the member 20 has a recessed socket 24 a for a screwinginstrument, and its front face 25 includes a cone with a rounded apex.

The implant according to this embodiment is intended to be used when thebody 10 is filled relatively densely with bone grafts. As the member 20is being screwed into the body 10, in addition to reinforcing theanchorage obtained with the aid of the thread 22, the member compressesthe bone grafts situated in the body 10 so as to stress these bonegrafts in particular in the direction of the overlying and underlyingvertebral plateaus and for improving fusion.

FIGS. 24 to 27 illustrate a fifth embodiment of the invention. The body10 of the implant has a cylindrical through-opening 101 a at the distalend 101 that is arranged on the axis of the body. The proximal end ofthe body has an opening that is not threaded.

The anchorage reinforcement member 20 is a screw having a wide thread.At its front end the screw, has a shaft-like extension made up of twoessentially semicylindrical axial lugs 29 a, 29 b which, at theirrespective free ends, have an added thickness 291 a, 291 b.

The two lugs 29 a, 29 b have an external diameter which is slightlysmaller than the diameter of the opening 101 a of the body 10. The lugsare also thinner so that their elastic deformability allows the member20 to be snapped into the body 10 before it is fitted by the surgeon.Thus, the member 20 is immobilized against translation, but is free inrotation. The member 20 is guided, on the one hand, by the opening 101 aand on the other hand, by the inner faces of the two branches 102, 103of the body 10.

Another important feature of the embodiment shown in FIG. 24 is that themember 20 is delimited by two flats 201, 201′, respectively, whichconfer upon the member a thickness which is substantially equal to thethickness of the body 10, all along the length of the body 10.

The threads form a sharp angle at the transition between the thread 22(of square cross-section) and the flats 201, 201′.

Furthermore, as in some of the preceding embodiments, the proximal part24 of the member 20 is provided with a recessed socket 24 a for ascrewing instrument.

The surgeon fits the implant in place using the following procedure. Thecomplete implant, that is to say the body 10 enclosing the member 20which has first been clipped on, and which has been given the angularorientation in FIG. 24, is engaged by impaction into the intervertebralspace. This operation is facilitated by the fact that the member 20 doesnot protrude beyond the limits of the body 10. The member 20 is turnedabout its axis with the aid of an appropriate instrument engaged in thesocket 24 a, so that the sharp edges of the threads 22 attack the bonematerial of the overlying and underlying vertebral plateaus, in this waytearing off bone chips that will fill the free spaces existing betweenthe body 10 and the member 20, so as to contribute to the bone fusion.

Because the member 20 is immobilized against any translation relative tothe body 10, and cannot therefore be screwed into the latter or into thevertebral plateaus, the threads 22 are advantageously given a widehelical pitch so that the screwing action favors a reciprocal sliding ofthe threads 22 relative to the vertebral plateaus, without inducing anaxial force sufficient to displace the implant in this direction.

Referring to FIGS. 28 to 32, in another preferred embodiment of thepresent invention, an implant includes a wide body 10 that is designedto receive two anchorage reinforcement members, 20 a and 20 b,respectively. To this end, the body 10 is widened and has two lateralbranches 102 and 103 as well as an intermediate middle branch 109extending between the branches 102 and 103.

The branches 102 and 109 define a first seat for the member 20 a, whilethe branches 103 and 109 define a second seat for the member 20 b. Theaxes of the two seats are mutually parallel, but being able, ifappropriate, to adopt a certain inclination. These two seats preferablyhave the same configuration as the single seat of the third embodiment,and the members 20 a and 20 b are preferably similar to the member 20 ofthis same embodiment.

The body 10 is provided with bone anchorage teeth 105, 105′.

As shown particularly in FIGS. 30 and 31, the upper and lower faces 104and 104′ of the body 10 have a dual inclination, one corresponding tothe faces coming closer together in the direction towards the distalends of the seats, and the other corresponding to the faces comingcloser together in a lateral direction (from right to left in FIG. 30).An opposite inclination can be obtained by turning the body 10 around.

This dual inclination allows the body 10 to be implanted at a slantwhile re-establishing the lumbar lordosis in the sagittal plane.

Furthermore, the increased width of the implant ensures a more stablesupport between the two vertebral plateaus, while the presence of twoanchorage reinforcement members 20 a and 20 b reinforces the resistanceto slipping relative to these plateaus.

As is evident to one skilled in the art, this variant of the inventioncan be applied to all the other implants described in the presentdocument, with a simple adaptation of the body 10.

Referring now to FIGS. 33 to 44, a description will be given of anothervariant of the implant which was described with reference to FIGS. 16 to19.

According to this variant, the outer body 10 of the implant comprises,in the same way as before, a general U shape with two lateral branches102 and 103 connected via a distal end wall 101, with roundedtransitions.

To increase the width of the implant, and hence to improve itsstability, the lateral branches 102 and 103 have, in the lateraldirection, a thickness which is substantially greater than that of thebranches 102 and 103 described with reference to FIGS. 16 to 19.

This thickness is preferably chosen in such a way as to give the overallwidth of the implant a value which is, for example, equal to about 1.5to 2.5 times the diameter of the anchorage reinforcement member 20.

In addition, to further improve the bone fusion between the overlyingand underlying vertebral plateaus, oblong through-openings 110 and 111are provided which extend, for example, vertically between the upperface 104 and the lower face 104′ of the body, in such a way that thelateral branches 102 and 103 each have a double wall. Also formed ineach of these walls are generally horizontal oblong openings 106, 106′,and 107, 107′, respectively, which allow the internal space of the body10 to open laterally to the outside of the body, by passing through thetwo double walls and the through-openings 110, 111, respectively.

Referring to FIGS. 43 and 44, the upper and lower faces 104 and 104′ ofthe body have a dual inclination relative to each other, in the lateraldirection and from the proximal end towards the distal end.

The anchorage reinforcement member 20 has a construction similar to thatwhich was described with reference to FIGS. 16 to 19. It has an internalfork having two branches 21 and a helical band 22 forming a boneanchorage thread attached to the branches. The parts 21 and 22 arepreferably made in one piece.

The thread 22 is preferably a self-tapping thread, which makes itpossible to screw directly into the overlying and underlying vertebralplateaus without having to form a tapping in these vertebral plateausprior to fitting. To this end, the thread 22 has, in its distal endregion, a radial section 22 b in the form of an outwardly turned point,and this section varies progressively, for example by about a fractionof a turn, up to a rectangular radial section 22 c. In addition, thediameter of the thread 22 increases progressively from its distal end upto the part of rectangular section, which is here of constant diameter.

The outer faces of the branches 21 are tapered, the diameter decreasingfrom the proximal end towards the distal end.

The two branches are joined at the area of a bushing 24 which is in theform of a cylindrical ring, formed preferably in one piece with thebranches.

A plug 30 having a series of flexible locking tabs 33, e.g. two pairs oftabs, can be mounted in this bushing 24 by being clipped in elasticallyfrom the outside. The tabs engage in the central opening of the bushing24, and the ends of which tabs, in the form of teeth 33 a, can catchonto the internal edge of the bushing 24.

The member 20 and its plug 30 are made integral in terms of rotation bymeans of the fact that each pair of tabs 33 tightly encloses the startof a respective branch 21 of the fork.

The plug 30 also has a centrally arranged tapped bore 34 adapted toreceive a threaded rod-shaped end of an instrument (not shown) forfitting the member 20.

Referring to FIGS. 40 and 44, two diametrically opposite notches 35 areformed on either side of the tapped bore 34, to permit angular indexingof the abovementioned instrument, in this case equipped withcomplementary arrangements, relative to the plug 30 and, thus, to thewhole of the anchorage reinforcement member 20.

Referring to FIG. 44, the thread 108 permitting screwing cooperationbetween the outer body 10 and the member 20 is provided only on one ofthe lateral branches of the body, in the form of a reentrant flangeending in a generally rectilinear edge 108 a.

Referring to FIGS. 33, 38 and 40, the end of the thread 22 on theproximal side is deformed, as indicated at 22 d. The deformation isformed in the direction of the adjacent thread turn, that is to saytowards the distal end.

This deformation makes it possible to give the thread 22 an immobilizingfunction against reverse rotation, and thus to prevent any risk of theanchorage reinforcement member 20 coming loose from the body 10 afterfitting, but before bone fusion.

Referring to FIGS. 33 to 44, the implant is fitted in place by fillingthe openings 110 and 111 of the body 10 with material promoting bonegrowth, such as bone grafts. The body is then inserted into theintervertebral space, if necessary after distraction. The anchoragereinforcement member 20 is filled with a material promoting bone growth,and this member 20 is then closed at its proximal end by the plug 30being clipped in. By means of screwing, the member is engaged in thealready fitted body. The tapered shape of the two branches 21 of thefork makes it possible, as the member 20 advances, to compress the bonegrowth material and thus to ensure good contact with the overlying andunderlying vertebral plateaus and with the bone growth material placedin the openings 110 and 111, via the openings 108 and 109.

The implants of the present invention are preferably made of abiocompatible material of suitable strength, such as a titanium alloy orstainless steel.

The surgeon is preferably offered implants according to the invention inthe form of a set of implants of different shapes and dimensions, makingit possible for a surgeon to choose an implant, and in particular thebody 10, best suited to the anatomy of the implantation site.

Implants can be provided in which the bodies 10 have different heights.Because of the different body heights, the diameter of the member 20 mayvary so that it works effectively with the selected body 10. Implantscan also be provided in which the bodies have different widths. Thus, inthe particular case of the third embodiment, it is possible to provide arange of implants whose widths vary progressively between a minimumwidth (e.g. FIGS. 16 to 19) and a maximum width (e.g. FIGS. 33 to 44),by varying the thickness, in the lateral direction, of the lateralbranches 102 and 103 of the body, while at the same time maintaining thesame size of internal space and also being able to use the same member20 in all cases. These lateral branches 102, 103 preferably vary from asingle wall (FIGS. 16 to 19) to a double wall (FIGS. 33 to 44) once thethickness of the branches 102, 103 has become sufficient to allow thevertical through-openings 110 and 111 to be made. Implants may also beprovided whereby the bodies have upper and lower faces of differentmutual inclinations, both from the front towards the rear and alsolaterally, with members 20 of identical or different diameters. Implantsmay also be provided whereby the bodies 10 and/or the anchoragereinforcement members 20 have different lengths, and in which theanchorage reinforcement members have different anchorage projections,and in particular of greater or lesser depth and greater or lesserspacing, depending on the mechanical characteristics encountered in thevertebral plateaus, etc.

The present invention is in no way limited to the embodiments describedabove and illustrated in the drawings, and one skilled in the art willbe able to vary or modify the embodiments in accordance with the spiritof the invention, and in particular will be able to combine theparticular features of the various embodiments described.

Furthermore, the bone anchorage projections such as have been describedabove can include any structure permitting mechanical anchorage and/orbone connection with the overlying and underlying vertebral plateaus. Inparticular, this can be a porous coating or hydroxyapatite.

1. A spinal implant comprising: a hollow body having a leading end, atrailing end and a pair of lateral walls extending from said leading endto said trailing end, said lateral walls including concave, non-threadedinner surfaces defining an internal space of said hollow body; and ananchoring member insertible between said lateral walls and into saidinternal space of said hollow body, said anchoring member having boneanchoring projections defining an outer diameter of said anchoringmember, wherein when said anchoring member is inserted into saidinternal space of said hollow body, said concave inner surfaces of saidlateral walls substantially conform to said outer diameter of saidanchoring member.
 2. The implant as claimed in claim 1, wherein saidhollow body has a distal wall extending between said lateral walls atsaid distal end thereof.
 3. The implant as claimed in claim 2, whereinsaid distal wall has a threaded bore extending at least partiallytherethrough.
 4. The implant as claimed in claim 2, wherein said distalwall has a curved outer surface that is located at said leading end ofsaid hollow body.
 5. The implant as claimed in claim 1, wherein saidhollow body is U-shaped with a closed leading end and an open trailingend.
 6. The implant as claimed in claim 1, wherein said internal spaceof said hollow body has a substantially cylindrical shape that isdefined by said concave inner surfaces of said lateral walls.
 7. Theimplant as claimed in claim 1, wherein said concave inner surfaces ofsaid lateral walls define a circular opening at the trailing end of saidhollow body.
 8. The implant as claimed in claim 1, wherein at least oneof said lateral walls has a reentrant thread at the trailing end of saidhollow body.
 9. The implant as claimed in claim 1, wherein said hollowbody has upper and lower faces extending between said leading andtrailing ends of said hollow body.
 10. The implant as claimed in claim9, wherein said upper and lower faces are angled relative to one anotherbetween said leading end and said trailing end of said hollow body. 11.The implant as claimed in claim 9, wherein at least one of said faceshas bone anchoring projections.
 12. The implant as claimed in claim 11,wherein said hollow body has a longitudinal axis that extends betweensaid leading end and said trailing end thereof and said bone anchoringprojections on said hollow body extend in a direction that traversessaid longitudinal axis of said hollow body.
 13. The implant as claimedin claim 1, wherein said lateral walls have convex exterior surfaces.14. The implant as claimed in claim 1, wherein each of said lateralwalls has a cross-section that is C-shaped.
 15. The implant as claimedin claim 1, wherein at least one of said lateral walls has an openingextending therethrough.
 16. The implant as claimed in claim 1, whereinsaid bone anchoring projections of said anchoring member comprisethreads.
 17. The implant as claimed in claim 16, wherein said trailingend of said hollow body has a circular opening that is bordered by areentrant thread formed on at least one of said lateral walls and saidthreads of said bone anchoring projection are adapted to cooperate withsaid reentrant thread for allowing said anchoring member to be screwedinto said internal space of said hollow body.
 18. The implant as claimedin claim 1, wherein said threads on said anchoring member define anexternal diameter and said concave inner surfaces of said lateral wallsdefine an internal diameter that substantially conforms to said externaldiameter.
 19. The implant as claimed in claim 1, wherein said anchoringmember has a hollow core and said bone anchoring projections surroundsaid hollow core.
 20. The implant as claimed in claim 1, furthercomprising a bone-growth inducing material provided in said internalspace of said hollow body.
 21. A spinal implant comprising: a hollowbody having a leading end, a trailing end and a pair of lateral wallsextending from said leading end to said trailing end, said lateral wallsincluding concave, non-threaded inner surfaces defining an innerdiameter of said hollow body; and an anchoring member insertible betweensaid lateral walls of said hollow body, said anchoring member havingthreads defining an outer diameter of said anchoring member, whereinsaid outer diameter of said anchoring member substantially matches saidinner diameter of said hollow body so that when said anchoring member isinserted into said hollow body said concave inner surfaces of saidlateral walls at least partially surround and substantially conform tosaid outer diameter of said anchoring member.
 22. The implant as claimedin claim 21, wherein said anchoring member has a hollow core surroundedby said threads of said anchoring member.
 23. The implant as claimed inclaim 22, further comprising a bone-growth inducing substance providedin said hollow core of said anchoring member.
 24. A spinal implantcomprising: a U-shaped hollow body having a closed leading end, an opentrailing end and a pair of lateral walls extending from said leading endto said trailing end, said lateral walls including concave, non-threadedinner surfaces defining an internal space of said hollow body; saidhollow body having upper and lower faces extending between leading andtrailing ends thereof and bone anchoring projections provided on saidupper and lower faces; and an anchoring member insertible between saidlateral walls and into said internal space of said hollow body, saidanchoring member having threads provided on an outer surface thereof,wherein when said anchoring member is inserted into said internal spaceof said hollow body said concave inner surfaces of said lateral wallssubstantially conform to said outer surface of said anchoring member.